Heather Mubarak says there are two secrets to her top-selling toffee. The first is its balance between sweet and salty flavors and the second is its texture, which is pleasingly crunchy but not tooth-shattering.

Although the 42-year-old mother of three refused to share her toffee recipe with Martha Stewart, she has happily shared the results with the candy-buying public. Since launching The Toffee Box in Carlsbad in 2009, her gourmet candy is now sold in more than 500 stores statewide, and the company was recently acquired by BBX Sweet Holdings, a subsidiary of BBX Capital for an undisclosed price. Mubarak will stay on as sales director.

The popular toffee — sold in square green gift boxes at Vons, Safeway, Whole Foods and many other retailers — has been in the Mubarak family for decades. Heather, who grew up in Solana Beach, first encountered the candy when she was 18, and her future husband, Jason Mubarak, invited her to join his family’s Christmas celebration in Rancho Santa Fe.

His grandmother developed the recipe and each Christmas his mother would stir up a large batch on the stove, then pour it out to cool on the kitchen’s granite countertop.

“Every time someone would walk by the counter, they’d break off a piece from this big slab. Every year without fail, it would all be gone by the end of the night,” she said.

After they married 20 years ago, Heather and Jason would spend two weeks every December cooking more than 50 pounds of grandma’s classic dark chocolate toffee for holiday gifts to family and friends. And every year, with few exceptions, the recipients would encourage the couple to market the tasty treats for sale.

With three young daughters to raise, she couldn’t commit the time to a home-based business. But once her two older daughters, Avery and Ella, were in school, and her toddler, Alden, was settled into a napping routine, she started researching the idea.

Mubarak had a background in selling women’s clothing and her husband is a financial manager with Morgan Stanley. So, armed with her marketing and entrepreneurial skills, his business knowledge and grandma’s recipe, The Toffee Box was born in January 2009.

In the early months, Mubarak cooked and packaged everything herself in a commercial kitchen that she rented on nights and weekends while her husband cared for the children at home. Initially, she sold the toffee through a website and by email to friends.

She also sent a box of her dark chocolate toffee to the producers of Rachael Ray’s television show. They were so impressed that Ray pitched the product as “snack of the day” on her Nov. 16, 2009, telecast. The following year, the toffee won a gold medal at the Los Angeles Luxury Chocolate Salon on TasteTV.

Heather Mubarak, of The Toffee Box, boxes some of her toffee for shipping.

Heather Mubarak, of The Toffee Box, boxes some of her toffee for shipping.

In 2010, Mubarak landed her first of many wholesale clients, Harvest Ranch Market in Encinitas, which has carried the candy ever since.

“We’ve seen her grow her business over the years and we’re honored to have been the first retailer to carry it,” said store manager Lisa Philbrook. “The product tastes great and it has beautiful packaging. We display it prominently in our store and we often get people coming in who ask for the beautiful green box. We love to support local companies and her product has done really well.”

To keep up with sales demand a few years ago, Mubarak outgrew her Carlsbad kitchen and contracted her toffee manufacturing to a confectioner in the L.A. area. She has also gradually expanded the product line to include mocha hazelnut (made with Starbucks coffee), milk chocolate pecan and white chocolate macadamia nut. Her personal favorite is dark chocolate almond, made with Guittard dark chocolate and chopped California almonds. A sixth flavor is now in the testing stage. Mubarak wouldn’t divulge the secret ingredient of new flavor other than to say it won’t be bacon. The toffee sells for $25 to $26 a pound.

In 2012, she was invited to cook her milk chocolate pecan toffee on television with Martha Stewart. The only catch was that the cooking segment would require divulging the recipe to viewers, which Mubarak wouldn’t do. Instead, Stewart promoted the toffee (which she called “unbelievably delicious”) on her show.

Over the years, Mubarak has signed up more than a dozen retailers, including Whole Foods, Jimbo’s, Major Market, Cardiff Seaside Market and Sur la Table.

In June, she added Vons and Safeway, which have more than 500 stores combined. She won’t divulge sales figures but said the company has grown by 40 percent each year.

Since the beginning, Mubarak has managed the business on her own, running sales, marketing, invoicing and distribution from a small office at her Carlsbad test kitchen on Loker Avenue West. This month, she agreed to sell the company’s assets to BBX, but The Toffee Box will remain headquartered in Carlsbad and she will stay on as its sales director.

BBX Capital President Jarett Levan describes Toffee Box as a premiere candy brand that his company plans to develop.

“We are excited about the growth in new products, distribution channels and geographies,” he said, in a statement.

Now that Mubarak has been freed from management duties, she said she’s looking forward to focusing on promoting the brand and helping expand sales.

Fall is high season for The Toffee Box — 75 percent of sales are during the holiday season — so Mubarak said she can’t carry on the family tradition of cooking a batch of toffee for Christmas. But she will bring home a few boxes to share with her husband and three daughters, now ages 7 to 13.

“I still love eating toffee,” she said. “And it wouldn’t be Christmas without it.”